It is possible to distinguish between various concepts in the case of supporting elements as are used these days in the fabrication of rotating electrical machines.
The first concept relates to machines whose winding is formed from already completely insulated conductor bars or coils, which are thus stiff and can be pressurized. In this case, fixed supporting rings are generally used, composed, for example, of thermoplastic or thermosetting plastic, which is generally reinforced. The supporting rings support the end winding from the outside and inside. In order to protect the conductors on the contact surfaces between the supporting ring and the conductor, plastic or elastic intermediate layers are generally used, which are generally curable, in some cases may be impregnated, and may be equipped to have a semiconducting capability. The supporting rings are generally braced with respect to the end winding by means of wedge systems.
In machines in which the complete stator is subjected to impregnation, a different supporting concept is used. Here, glass threads, that is to say threaded glass rovings or filled glass flexible tubes, that is to say axially bundled, unidirectional or knitted glass rovings, form a casing around the flexible tubes composed of woven glass rovings, and are introduced into an end winding in an annular shape. These threads or flexible tubes are impregnated during the impregnation of the stator and, when cured, form a fixed, radial supporting ring, which also provides the support and spacing between the individual conductors when laid in the form of plugs or loops.
Finally, in a third supporting concept for end windings of fully insulated windings, pressure-resistant flexible tubes, such as fire-service hoses, are used, which are laid in a suitable manner around the end winding in the dry state, in a similar way to the threads described above. In this case, the flexible tubes are simply placed just in an annular shape around and in the end windings, where they are then fixed by other elements, or they may be looped through between the conductors or plugged between the conductors. Once everything is ready, the flexible tube is filled with a low-viscosity resin or a resin with fillers in the form of powders or fibers and which is preferably cold-cured. After curing, solid rings are formed, which are optimally matched to the shape of the end winding.
However, all these supporting concepts mentioned above have certain disadvantages.
In the first supporting concept, a relatively large amount of manual work is required or, in some cases, it may be necessary to work with materials that are problematic in terms of health and safety at work, for example glass nonwoven or binder resins. Furthermore, the curing of binding agents is time-consuming, and may even require an additional heating process. In addition, the use of cold-curing intermediate layers may lead in operation, that is to say in the event of heating, to the prestressing of the supporting rings against the conductors becoming weaker due to creeping of this material when subject to continuous mechanical loading, thus resulting in the end winding having a tendency to oscillate and vibrate.
In contrast, the main disadvantage of the second concept is the need for impregnation. In machines in which this impregnation is impossible, this variant is not feasible or must be replaced by the injection of resin, which is dubious from the health and safety at work point of view, into the threads along the entire thread length, by means of spraying. The mechanical quality of the cured threads is, however, worse than in the case of vacuum-pressure impregnation since the resin penetration is inadequate owing to the large amount of air included.
Finally, in the third supporting concept, the mechanical stiffness of flexible tubes filled with pure resin is limited, particularly at relatively high temperatures, and very particularly for cold-curing resins. On the other hand, when filled resins are used, the processing capability is greatly limited since the fillers considerably increase the viscosity of the filling compound, so that only relatively short and kink-free flexible tubes can be filled without problems.